Pumps



1970 R. RAVENEL 3,523,002

I PUMPS Filed June I4, 1968 2 Sheets-Sheet 1 {i Hug: p lluln.

76 MAT la I I um 2 c- PI- Pa Raymond RAVEIEL Inventor Attorney 1970 R. RAVENEL 3,523,002

PUMPS Filed June 14, 1968 2 Sheets-Sheet 2 Raymond RAVENEL Inventor Attorney United States Patent 3,523,002 PUMPS Raymond Ravenel, Sceanx, France, assignor to Societe Anonyme Andr Citroen, Paris, France, a corporation of France Filed June 14, 1968, Ser. No. 737,043 Claims priority, application France, June 20, 1967, 3

3, 71 Int. Cl. F04b 9/10, 19/22, 7/00 US. Cl. 417534 2 Claims ABSTRACT OF THE DISCLOSURE A pump assembly includes a shaft-power driven piston operating in a first cylinder and a free piston operable in a second cylinder. A pair of ducts provide intercommunication between the cylinders at opposite ends thereof and each duct has an intake valve and an outlet valve. In a modification the intake and outlet valves are replaced by ports in the second cylinder which cooperate with passages and ports in the free piston.

The present invention relates to a pump with a high power-to-weight ratio.

SUMMARY OF THE INVENTION This pump comprises one pair of chambers, between which a moving member, such as a piston, provides a fluid-tight separation. Means is provided whereby reciprocating motion can be imparted to the moving member; the chambers of a second pair are separated from one another by a freely moving member, each chamber of BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of one embodiment of a pump in accordance with the invention;

FIG. 2 is a velocity diagram for the two pistons of the pump shown in FIG. 1;

FIGS. 2a, 2b and 2c are different forms of the diagram of FIG. 2;

FIG. 3 is a graph indicating the displacements with time of the two pistons;

FIG. 4 is a diagram illustrating the variation in power as a function of the difference between the inlet and outlet pressures; and

FIG. 5 is a view, similar to FIG. 1, of a second embodiment in accordance with the invention.

As shown in the drawing, the pump comprises a casing 1, including two cylinders 2 and 3, intercommunicating at their ends through two ducts 4a and 4b.

A piston 5, keyed to a rod 6 is slidable within the cylinder 1, the rod being coupled with a driving shaft 7 by a crank 8 and a connecting rod 9.

A free piston 10, having the same cross-sectional area S as the piston 5, slides within the cylinder 3.

Each of the ducts 4a and 4b is connected through an inlet valve 11a or 1112 respectively (which may or may not be spring-loaded) to an intake 12, in which the fluid to be pumped is at a pressure of P Each duct 4a, 4b

3,523,002 Patented Aug. 4, 1970 also communicates through a delivery valve 13a or 13b respectively (which may or may not be spring-loaded), with an outlet 14, in which the pumped fluid is at a pressure P The latter pressure is assumed to be held constant by a hydraulic receiver connected to it.

Assuming the shaft 7 to be driven at constant speed, fluid will be drawn from the inlet 12 and delivered into the outlet 14, as explained below. In what follows, the total volume enclosed within the duct 4a and those chambers of the cylinders 2 and 3 which are in communication with it will be designated V while the total volume enclosed within the duct 4b and those chambers of the cylinders 2 and 3 Which are in communication with it will be designated V The piston 5 derives its motion from the rotation of the shaft 7. Its speed variation with time is represented by the curve 15 (FIG. 2), which is substantially sinusoidal. The convention adopted in this diagram is that the piston speed is positive when the piston is moving from right to left.

Again, one side of the free piston 10 is subjected to the intake pressure P while the other side is subjected to the delivery pressure P The force acting on this piston 10 is therefore constant, its value being (P P )S, this force being exerted first in one direction and then in the other direction. Hence, the curve representing the speed variation with time of this piston is made up of a series of straight lines symmetrical with reference to the time axis, the convention adopted being that the speed of the free piston is positive when that piston is moving from left to right. The slope of these straight lines represents the acceleration 'y of the free piston and is equal to 1 Po M M being the mass of the free piston.

During steady conditions, the movements of the driving piston 5 and those of the free piston 10 are synchronized and the curves representing their speed variations with time can be drawn on the same diagram.

Thus, the cycle of the two motions is the same. Moreover, at the moment of change-over, that is to say when the functions of the ducts 4a and 4b are inverted, the force acting on the free piston 10 passes through zero and changes direction. This change-over therefore takes place at the moment of inversion of acceleration, in other words, at the peak of the graph giving the speed of the free piston. Moreover, during the change-over, the flowof fluid taken in and delivered is nil, so the speed of the free piston at that moment is equal to that of the driving piston, since the cross-sectional area of both pistons is the same. The peaks of the graph showing the speed of the free piston 10 thus lie on the curve giving the speed of the piston 5.

On the curve indicating the velocity of the piston 5; two lines parallel to the axis of the abscissae (time axis) can be drawn, having as ordinates the maximum values of the free piston speed (the values of these being i (Po-P1) 2%} T being the period of movement of the driving piston S). It will then be found that the curve 16 can be drawn either with peaks at A, B, C and out of phase to the ex tent of with the curve 15, or the curve 16' with peaks at A, B, C' and D' and out of phase to the extent of with the curve 15.

However, the curve 16 represents an impossible mode of operation. This is because, starting from B, where the flow of fluid is nil, the speed of the driving piston 5 is positive and greater than that of the free piston 10, which is also positive. Hence, the volume V grows smaller,

causing the fluid to be driven at the pressure P while the volume V increases and causes the fluid to be drawn in at the pressure P The free piston is thus subjected to a force acting in the direction of the positive speeds, so that its acceleration is positive and its speed should increase, which is contrary to what the curve 16' indicates.

On the other hand, starting from B, the speed of the free piston 10 is higher than that of the driving piston 5, both speeds being positive. The space V, is therefore .increasing in volume and contains fluid at the pressure P while the space V is diminishing and contains fluid at the pressure P The free piston is thus subjected to a force which is negative, so that its speed drops; and this is indicated by the curve 16.

FIG. 2 therefore, shows the speed of the driving piston 5 at 15 and that of the free piston at 16.

From the velocity diagram of FIG. 2, a diagram showing the motions of the two pistons can be derived, bearing in mind that FIG. 2 shows the maximum stroke of the free piston 10 to be smaller than that of the driving piston 5, the strokes of both pistons being represented by the areas subtended by the curves and 16. The curve representing the movement with time of the driving piston 5 is indicated at 17 in FIG. 3 and consists of a sine wave, whereas the curve representing the movement of the free piston is designated 18 and is made up of a series of parabolic arcs. It will be observed from this figure that the motion of the free piston is retarded in relation to that of the driving piston and that the change-over takes place when the free piston 10 is at the mid-point in its stroke.

The cross-sectional area of both pistons being the same, the flow of fluid delivered into the outlet 14 is proportional at any moment to the difference between the ordinates of the curves 15 and 16 for the moment in question. Hence, the volume of fluid delivered at each half-cycle is represented by the area a bounded by the sinusoidal arc and the corresponding straight line AB. Moreover, as already stated, the difference between the delivery pressure P and the intake pressure P is proportional to the slope 'y of the straight-line sections. The power of the pump is thus proportional to the product 17.

From the velocity diagram of FIG. 2, therefore, one can seen how the power of the pump varies with the pressure difference P P Should this pressure difierence be nil, the curve 16 is reduced to the axis of the abscissae and the rate of de livery 16 is at its maximum, but the power is nil. When the pressure difference increases, the rate of delivery falls, but initially the pressure increases.

There is one pressure difference at which the sections of the curve 16 are tangential to the sine wave 15 (FIG. 2a). Should the pressure difference continue to increase, the flow of fluid delivered ceases to be continuous.

In point of fact, a velocity diagram in which the sections of the curve 16 intersect the since wave 15 (FIG. 2b) cannot exist, since from B to I the two pistons have a positive speed, that of the driving piston 5 being greater than that of the free piston 10. The space V must therefore diminish in volume, fluid being driven at the pressure P while the volume V increases and fluid is drawn in at the pressure P The acceleration of the free piston 10 is thus positive and its speed should rise, which is contrary to what the graph indicates.

FIG. 2c is a velocity diagram in which the pressure difference is higher than in FIG. 2a and which is not impossible. In this diagram, the tangent to B cuts the sine wave 15 at a point C, the ordinate of which is negative and larger in absolute value than that of B. The flow of fluid is nil from C to C; during this time, the free piston 10, instead of its movement accelerating uniformly, has sinusoidal motion and moves in synchronism with the driving piston 5.

The pressure difference may increase further until the section BC comes to coincide with the tangent to the sine wave at the point Tom the axis of the abscissae; but then the area a and hence the flow of fluids are nil. The same applies to the power.

Thus, as the pressure difference rises from zero, the power P supplied by the pump increases to a peak and then falls to zero, as shown in curve 19 in FIG. 4, in which the point B corresponds to the velocity diagram given in FIG. 2a.

It has been assumed in the foregoing, for the sake of simplicity, that both pistons 5 and 10 have the same crosssectional area. This need not be so, of course, and it is possible to give a similar explanation of the operation of a pump in accordance with the invention by considering not the velocity diagrams, but diagrams showing the flow of fluid displaced at any given moment by each of the pistons.

It will be clear, from what has been stated, that by increasing the frequency, the delivery and hence the power of the pump are increased. However, this increase in frequency also enables the pressure difference to be increased, thereby further increasing the power output. It can readily by demonstrated graphically, in fact, that if the waves in the curve 15 close together, the slope of the sections of the curve 16 must be increased to get the same area a, that is to say the same rate of delivery per cycle.

The operating frequency of the pump illustrated in FIG. 1 is limited by the operation of the valves 11a, 11b, 13a and 13b to a value of the order of cycles per second.

The modification shown in FIG. 5 can be used at higher speeds. In this figure, the valves have been dis spended with and the free piston 10' contains two internal passages, 21a and 21b. One end of each of these passages openes into one of the chambers in the cylinder 3, while the other end opens to the periphery, approximately in the middle of the piston. The fluid intake pipe 12 is connected to two ducts, 22a and 22b, which open into the chambers in the cylinder 3 in such a position as to be substantially masked when the piston is in its mid-cylinder position, as shown in the drawing, and to be uncovered as piston moves from this central position away from the chamber concerned, which is thus placed in communication with the intake 12. The fluid outlet :14, on the other hand, is connected to two ducts, 23a and 23b, leading substantially to the middle of the cylinder 3, which are substantially masked when the piston is in its central position; and when the piston moves towards one of the chambers, the side aperture of the passage 21a or 21b connected with that chamber takes up a position facing the duct 23a or 23b, as the case may be, so that the chamber in question is placed in communication with the outlet 14.

As has already been shown, the change-over takes place when the free piston 10 is half-way along its travel. In the example shown in FIG. 1, this mid-position is not necessarily constant, but may vary in relation to the cylinder; in the modification shown in FIG. 5, on the other hand, the change-over takes place when the piston is in the middle of the cylinder and the position of the free piston is thus fixed.

In the example shown in FIG. 5, the operating sequence in which, at one stage, all the valves are closed is impossible, so the theoretical maximum pressure difference is that at which the slope of the sections of the curve 16 is as in FIG. 2a and the useful pressure curve is limited to the point B in FIG. 4.

The invention should naturally not be regarded as limited to the practical examples here described and illustrated; thus, all modifications thereof are included within its scope. For instance, the pistons 5 and 10 may be replaced by oscillating vanes or blades.

I claim:

1. In a pump,

means defining a first pair of chambers,

a movable member forming part of said means and forming a substantially fluid-tight partition between said chambers,

means for driving the movable member with a reciprocating motion,

means defining a second pair of chambers,

a freely movable member forming part of the means defining the second pair of chambers and forming a substantially fluid-tight partition between said chambers,

communication means extending between respective chambers of each pair of chambers,

means defining a fluid inlet to the pump,

means defining a fluid outlet from the pump, and

distribution means interposed between the fluid inlet,

the fluid outlet and the chambers, said freely mo-vable member being formed as a piston and constituting a slide of the distribution means, so constructed and arranged as to connect the fluid inlet to one of said sets of chambers in each of the extreme positions of said freely movable member and to connect the other set of said chambers to the outlet through said freely movable member.

2. A pump according to claim *1, wherein the movable a crank mounted on the shaft and a connecting rod coupled to the crank and to the piston.

References Cited UNITED STATES PATENTS 40,063 9/1863 Homme 103-44 1,109,108 9/1914 Chance et a1. 10375 1,032,114 7/1912 Chance et a1. 103-75 2,002,713 5/ 1935 Penick et a1. 103-44 2,833,226 5/1958 De Meux 103166 FOREIGN PATENTS 792,627 1/1936 France. 983,089 2/1965 Great Britain.

20 WILLIAM L. 'FREEH, Primary Examiner US. Cl. X.R. 

